The present invention relates to a torque converter and more particularly to a lock-up torque converter including a direct drive clutch.
Motor vehicles installed with an automatic transmission including a torque converter give an easy drivability but are poor in fuel economy because there is a slip within the torque converter between a pump impeller thereof and a turbine runner thereof. Therefore, there have been proposed lock-up torque converters in which during a certain operation mode such as high speed engine operation where engine cyclic torque variation is small and negligible, the turbine runner will be coupled directly with the pump impeller to prevent the occurrence of slip in the torque converter thereby to improve fuel economy.
According to a lock-up torque converter disclosed in U.S. Pat. No. 3,497,043, a clutch piston drivingly connected to a turbine runner is engageable with the adjacent end wall of a converter cover secured to a pump impeller to provide a direct drive between the engine and transmission of a vehicle. Upon engagement of the clutch piston with the torque converter cover, a clutch chamber is formed therebetween. When the clutch chamber is pressurized, the clutch piston is urged against the torque converter pressure within a chamber formed by the converter cover and pump impeller out of engagement with the converter cover. When the clutch chamber is exhausted, the clutch piston is urged into engagement with the converter cover by the torque converter pressure. A lock-up control valve is provided for effecting clutch engagement or disengagement. A passageway extending partly through an output shaft communicates with the clutch chamber and with the lock-up control valve, while, another passageway extending between a stationary sleeve rotatably supporting the output shaft, and a pump driving sleeve communicates with the inside of the pump impeller and with the control valve. For effecting clutch disengagement, the control valve pressurizes the passageway communicating with the clutch chamber and exhausts the passageway communicating with the pump impeller so that a pressurized oil will flow from the clutch chamber toward the chamber of the torque converter assembly. Under a lock-up condition when the clutch engagement is required, the control valve exhausts the passageway communicating with the clutch chamber and pressurizes the passageway communicating with the pump impeller so as to create a pressure difference across the clutch piston urging the latter into engagement with the converter cover.
With the control system employed by this known torque converter, since communication between the chamber enclosing the torque converter and the clutch chamber is closed upon engagement of the clutch piston with the converter cover, the oil is confined within the chamber enclosing the torque converter and thus can not be used for lubrication of various parts of the torque converter under lock-up condition. This means that this control system must be provided independently from the conventional lubrication system.
Another problem with the known torque converter is derived from the above mentioned fact that the oil is confined within the chamber enclosing the torque converter assembly under lock-up condition which means that the oil within the torque converter can not be cooled under lock-up condition so that if the oil temperature is hot immediately before plunging into lock-up condition, the temperature within the torque converter assembly will be held high under lock-up condition.